1. Field of the Invention
The present invention relates to an ink jet printing apparatus. More specifically, the present invention relates to a system for minimizing an effect the mist of ink, processing liquid for rendering the ink insoluble or insolubilized substance has on an ejection performance of print heads during a printing process that uses the ink and the processing liquid, the mist being produced as a result of injecting the ink and the processing liquid.
2. Description of the Related Art
The processing liquid that renders ink insoluble basically contributes to improving the water resistance of a printed image. The processing liquid is ejected onto the same areas of a print medium where the ink droplets have landed so that droplets of the processing liquid overlap the ink dots, or onto those areas adjacent to the ink dots so that they partly contact the ink dots. The resulting mixing of the ink and the processing liquid causes a colorant in the ink to become insoluble. The ink fixed on the print medium in this way has improved water resistance because of its insolubility.
In addition to this purpose, the processing liquid is also used to improve the quality of a printed image. In this regard, the applicant of this invention has made a variety of proposals. For example, the processing liquid is effective for preventing feathering and spreading of ink and for improving the density.
The processing liquid is ejected by using ordinary print heads similar to those used for ink. In the case of a serial type printer, for example, a processing liquid head is mounted on a carriage along with black, cyan magenta and yellow heads. As the carriage moves, the ink or the processing liquid is ejected onto the print medium from respective heads in the order of their arrangement. In a printer with so-called full-line type heads each having ejection nozzles arrayed over a range corresponding to a width of the print medium, the processing liquid head and the ink ejecting heads are arranged at predetermined intervals in the print medium feed direction. The processing liquid is ejected after each feeding of the print medium, resulting in the processing liquid being mixed with the ink on the print medium as described above.
In the ink jet printing apparatus using the processing liquid, however, because the processing liquid renders the ink insoluble, insolubilized substances not directly involved in the printing are produced and may have a variety of adverse effects on the printing.
To describe in more detail, when the processing liquid is ejected from the head, not only are droplets formed that are intended to land on the print medium but much smaller droplets or mist are also produced. The mist of the processing liquid, because it has relatively small mass and speed, may not reach the print medium but float and adhere directly to the nozzle surfaces of other heads. The nozzle surface is a surface of the print head in which the ink ejection nozzles are arranged. When the floating mist of the processing liquid adheres to the nozzle surfaces and reacts with the ink in or around the nozzles to form insoluble substances, ejection troubles may arise such as ink ejection failures, insufficient amounts of ink ejected and deviations of ink ejection directions.
The processing liquid mist may also be produced by a part of the ejected processing liquid droplets bouncing off the print medium when they land on it. Such bounced-off mist of the processing liquid may adhere to other heads, leading to similar ejection failures.